2003 UB 313: A Tenth Planet? ... Credit Copyright: M. Brown ( Caltech ), C. Trujillo ( Gemini ), D. Rabinowitz ( Yale ), NSF , NASA Explanation: Has a tenth planet been discovered? A newly discovered object , designated 2003 UB 313 and located more than twice the distance of Pluto , is expected to be at least as large as Pluto and probably larger, given current measurements. ... If so, and if some are found closer in than 2003 UB 313 , it may be premature to call 2003 UB 313 the tenth planet. ...